On 09/18/2017 02:08 PM, Stefano Stabellini wrote:> On Fri, 15 Sep 2017, Greg KH wrote:>> On Thu, Sep 14, 2017 at 04:23:05PM -0700, Stefano Stabellini wrote:>>> Hi all,>>>>>> We are getting reports from Xen on ARM users about DMA issues. The>>> problem is that the commit below>>> (7e91c7df29b5e196de3dc6f086c8937973bd0b88) is necessary to support mmap>>> on Xen on ARM. It is self-contained and doesn't affect anything outside>>> of Xen on ARM, so I think is a good candidate for backporting. It went>>> upstream in 4.11.>> But it's a new feature, right? How does that fit the stable kernel>> rules?> It implements a previously unimplemented function (mmap), although it> calls the generic functions to do it. Yes, I agree with you that it> can be classified as a new feature. If that is against the stable kernel> rules, then please discard this request.>> FYI the reason why it didn't raise a flag in my mind is that users> reported something like "unhandled alignment fault (11) at> 0xffffa6048080, esr 0x92000061", which really looks more like a bug.>>>>> Could you please backport the following commit:>>>>>> commit 7e91c7df29b5e196de3dc6f086c8937973bd0b88>>> Author: Stefano Stabellini <stefano.stabellini@eu.citrix.com>>>> Date: Tue Feb 7 19:58:02 2017 +0200>>> >>> swiotlb-xen: implement xen_swiotlb_dma_mmap callback>>> >>> This function creates userspace mapping for the DMA-coherent memory.>>> >>> to the stable trees up until 3.14?>>>>>>>>> Because of 00085f1efa387a8ce100e3734920f7639c80caa3 "dma-mapping: use>>> unsigned long for dma_attrs", the appended patch (to be applied on top)>>> is required for trees older than 4.8. >> What does the kvm maintainers think about this?> That would be the Xen maintainers right? In that case, Boris, Juergen,> please let us know what you think.

This is a nop for x86 so it's safe from that perspective. I can't findmmap op for ARM though (xen_get_dma_ops(dev)->mmap).